Anatomical visualization system

ABSTRACT

An improved anatomical visualization system which is adapted to augment a standard video endoscopic system with a coordinated computer model visualization system so as to enhance a physician&#39;s understanding of the patient&#39;s interior anatomical structure A database defining a 3-D computer model comprises at least a first software object corresponding to the anatomical structure. A second software object having a surface is placed in registration with the first software object such that they coexist in a single coordinate system. A movable sensor, such as an endoscope, acquires a real-time video image which is texture mapped onto the surface of the second software object. A processing device is provided to generate an image from the first and second registered software objects taken from any specified point of view relative to the single coordinate system.

FIELD OF THE INVENTION

This invention relates to medical apparatus in general, and moreparticularly to anatomical visualization systems.

BACKGROUND OF THE INVENTION

Endoscopic surgical procedures are now becoming increasingly popular dueto the greatly reduced patient recovery times resulting from suchsurgery.

More particularly, in endoscopic surgical procedures, relatively narrowsurgical instruments are inserted into the interior of the patient'sbody so that the distal (i.e., working) ends of the instruments arepositioned at a remote interior surgical site, while the proximal (i.e.,handle) ends of the instruments remain outside the patient's body. Thephysician then manipulates the proximal (i.e., handle) ends of theinstruments as required so as to cause the distal (i.e., working) endsof the instruments to carry out the desired surgical procedure at theremote interior surgical site. As a result of this technique, theincisions made in the patient's body can remain relatively small,thereby resulting in significantly faster patient recovery times.

By way of example, laparoscopic surgical procedures have been developedwherein the abdominal region of the patient is inflated with gas (e.g.,CO₂) and then surgical instruments are inserted into the interior of theabdominal cavity so as to carry out the desired surgical procedure. Byway of further example, arthroscopic surgical procedures have beendeveloped wherein a knee joint is inflated with a fluid (e.g., a salinesolution) and then surgical instruments are inserted into the interiorof the joint so as to carry out the desired surgical procedure.

In order to visualize what is taking place at the remote interior site,the physician also inserts an endoscope into the patient's body duringthe endoscopic surgery, together with an appropriate source ofillumination. Such an endoscope generally comprises an elongated shafthaving a distal end and a proximal end, and at least one internalpassageway extending between the distal end and the proximal end. Imagecapturing means are disposed at the distal end of the shaft and extendthrough the shaft's at least one internal passageway, whereby the imagecapturing means can capture an image of a selected region locatedsubstantially adjacent to the distal end of the shaft and convey thatimage to the proximal end of the shaft. Viewing means are in turndisposed adjacent to the proximal end of the shaft, whereby the imageobtained by the image capturing means can be conveyed to a displaydevice which is viewed by the physician.

Endoscopes of the sort described above are generally sufficient topermit the physician to carry out the desired endoscopic procedure.However, certain problems have been encountered when using suchendoscopes in surgical procedures.

For example, endoscopes of the sort described above generally have afairly limited field of view. As a result, the physician typicallycannot view the entire surgical field in a single image. This can meanthat the physician may not see an important development as soon as itoccurs, and/or that the physician must expend precious time and energyconstantly redirecting the endoscope to different anatomical regions.

Visualization problems can also occur due to the difficulty of providingproper illumination within a remote interior site.

Also, visualization problems can occur due to the presence ofintervening structures (e.g., fixed anatomical structures, movingdebris, flowing blood, the presence of vaporized tissue when cauterizingin laparoscopic surgery, the presence of air bubbles in a liquid mediumin the case of arthroscopic surgery, etc.).

It has also been found that it can be very difficult for the physicianto navigate the endoscope about the anatomical structures of interest,due to the relative ambiguity of various anatomical structures when seenthrough the endoscope's aforementioned limited field of view and due tothe aforementioned visualization problems.

OBJECTS OF THE INVENTION

Accordingly, one object of the present invention is to provide animproved anatomical visualization system.

Another object of the present invention is to provide an improvedanatomical visualization system which is adapted to enhance aphysician's ability to comprehend the nature and location of internalbodily structures during endoscopic visualization.

Still another object of the present invention is to provide an improvedanatomical visualization system which is adapted to enhance aphysician's ability to navigate an endoscope within the body.

Yet another object of the present invention is to provide an improvedanatomical visualization system which is adapted to augment a standardvideo endoscopic system with a coordinated computer model visualizationsystem so as to enhance the physician's understanding of the patient'sinterior anatomical structures.

And another object of the present invention is to provide an improvedmethod for visualizing the interior anatomical structures of a patient.

And still another object of the present invention is to provide animproved anatomical visualization system which can be used with remotevisualization devices other than endoscopes, e.g., miniature ultrasoundprobes.

And yet another object of the present invention is to provide animproved visualization system which can be used to visualize remoteobjects other than interior anatomical structures, e.g., the interiorsof complex machines.

And another object of the present invention is to provide an improvedmethod for visualizing objects.

SUMMARY OF THE INVENTION

These and other objects of the present invention are addressed by theprovision and use of an improved anatomical visualization systemcomprising, in one preferred embodiment, a database of pre-existingsoftware objects, wherein at least one of the software objectscorresponds to a physical structure which is to be viewed by the system;a real-time sensor for acquiring data about the physical structure whenthe physical structure is located within that sensor's data acquisitionfield, wherein the real-time sensor is capable of being moved aboutrelative to the physical structure; generating means for generating areal-time software object corresponding to the physical structure, usingdata acquired by the sensor; registration means for positioning thereal-time software object in registration with the pre-existing softwareobjects contained in the database; and processing means for generatingan image from the software objects contained in the database, based upona specified point of view.

In another preferred form of the invention, the generating means createa software object that corresponds to a disk. The generating means mayalso be adapted to texture map the data acquired by the sensor onto thedisk. Also, the registration means may comprise tracking means that areadapted so as to determine the spatial positioning and orientation ofthe real-time sensor and/or the physical structure.

In another preferred aspect of the invention, the real-time sensor maycomprise an endoscope and the physical structure may comprise aninterior anatomical structure. The system may also include either userinput means for permitting the user to provide the processing means withthe specified point of view, or user tracking means that are adapted toprovide the processing means with the specified point of view.

According to another aspect of the invention, the real-timecomputer-based viewing system may comprise a database of softwareobjects and image generating means for generating an image from thesoftware objects contained in the database, based upon a specified pointof view. In accordance with this aspect of the invention, means are alsoprovided for specifying this point of view. At least one of the softwareobjects contained in the database comprises pre-existing datacorresponding to a physical structure which is to be viewed by thesystem, and at least one of the software objects comprises datagenerated by a real-time, movable sensor. The system further comprisesregistration means for positioning the at least one software object,comprising data generated by the real-time movable sensor, inregistration with the at least one software object comprisingpre-existing data corresponding to the physical structure which is to beviewed by the system.

A preferred method for utilizing the present invention comprises:(1)positioning the sensor so that the physical structure is located withinthat sensor's data acquisition field, and generating a real-timesoftware object corresponding to the physical structure using dataacquired by the sensor, and positioning the real-time software object inregistration with the pre-existing software objects contained in thedatabase; (2) providing a specified point of view to the processingmeans; and (3) generating an image from the software objects containedin the database according to that specified point of view.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention will bemore fully disclosed or rendered obvious by the following detaileddescription of the preferred embodiment of the invention, which is to beconsidered together with the accompanying drawings wherein:

FIG. 1 is a schematic view showing an anatomical visualization systemformed in accordance with the present invention;

FIG. 2 is a schematic view of a unit cube for use in defining pologonalsurface models;

FIG. 3 illustrates the data file format of the pologonal surface modelfor the simple unit cube shown in FIG. 2;

FIG. 4 illustrates a system of software objects;

FIG. 5 illustrates an image rendered by the anatomical visualizationsystem;

FIG. 6 illustrates how various elements of system data are input intocomputer means 60 in connection with the sytem's generation of outputvideo for display on video display 170;

FIG. 7 illustrates additional details on the methodology employed byanatomical visualization system 10 in connection in rendering a videooutput image for display on video display 170;

FIG. 8 illustrates a typical screen display provided in accordance withthe present invention;

FIG. 9 illustrates an image rendered by the anatomical visualizationsystem;

FIG. 10 is a schematic representation of a unit disk software objectwhere the disk is defined in the X-Y plane and has a diameter of 1; and

FIG. 11 shows how the optical parameters for an encdoscope can definethe relationship between the endoscope 90A' and the disk 90B'.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Looking first at FIG. 1, there is shown an anatomical visualizationsystem 10 which comprises a preferred embodiment of the presentinvention. Anatomical visualization system 10 is intended to be used bya physician 20 to visually inspect anatomical objects 30 located at aninterior anatomical site. By way of example, anatomical visualizationsystem 10 might be used by physician 20 to visually inspect a tibia 30A,a femur 30B and a meniscus 30C located within the knee joint of apatient.

An important aspect of the present invention is the provision of animproved anatomical visualization system which is adapted to augment astandard video endoscopic system with a coordinated computer modelvisualization system so as to enhance the physician's understanding ofthe patient's interior anatomical structure.

To that end, anatomical visualization system 10 generally comprisesendoscope means 40, endoscope tracking means 50, computer means 60,database means 70 containing 3-D computer models of various objectswhich are to be visualized by the system, and display means 80.

Endoscope means 40 comprise an endoscope of the sort well known in theart. More particularly, endoscope means 40 comprise an endoscope 90which comprises (i) a lens arrangement which is disposed at the distalend of the endoscope for capturing an image of a selected region locatedsubstantially adjacent to the distal end of the endoscope, and (ii) anappropriate image sensor, e.g., a charge coupled device ("CCD") elementor video tube, which is positioned on the endoscope so as to receive animage captured by the lens arrangement and to generate correspondingvideo signals which are representative of the captured image.

The video signals output from endoscope 90 are fed as an input intocomputer means 60. However, inasmuch as endoscope 90 will generallyoutput its video signals in analog form and inasmuch as computer means60 will generally require its video signal input to be in digital form,some conversion of the endoscope's video feed is generally required. Inthe preferred embodiment, video processing means 95 are provided toconvert the analog video signals output by endoscope 90 into the digitalvideo signals required by computer means 60. Video processing means 95are of the sort well known in the art and hence need not be described infurther detail here.

Endoscope tracking means 50 comprise a tracking system of the sort wellknown in the art. More particularly, endoscope tracking means 50 maycomprise a tracking system 97 of the sort adapted to monitor theposition and orientation of an object in space and to generate outputsignals which are representative of the position and orientation of thatobject. By way of example, tracking system 97 might comprise an opticaltracking system, an electromagnetic tracking system, an ultrasonictracking system, or an articulated linkage tracking system, among otheralternatives. Such tracking systems are all well known in the art andhence need not be described in further detail here. Tracking system 97is attached to endoscope 90 such that the output signals generated bytracking system 97 will be representative of the spatial positioning andorientation of endoscope 90. The output signals generated by trackingsystem 97 are fed as an input into computer means 60.

Computer means 60 comprise a digital computer 130 of the sort adaptedfor high speed processing of computer graphics. Such digital computersare well known in the art. By way of example, digital computer 130 mightcomprise a Silicon Graphics Reality Engine digital computer, or it mightcomprise a Silicon Graphics Iris Indigo² Impact digital computer, or itmight comprise some equivalent digital computer.

Computer means 60 also comprise the operating system software(schematically represented at 135 in FIG. 1) and the application programsoftware (schematically represented at 140 in FIG. 1) required to causecomputer 130 to operate in the manner hereinafter described. Inparticular, application program software 140 includes image renderingsoftware of the sort adapted to generate images from the 3-D computermodels contained in database means 70 according to a specified point ofview. By way of example, where digital computer 130 comprises a SiliconGraphics digital computer of the sort disclosed above, operating systemsoftware 135 might comprise the IRIX operating system, and the imagerendering software contained in application program software 140 mightcomprise the IRIS g1 image rendering software or the OpenGL imagerendering software. Such software is well know in the art. As is alsowell known in the art, such image rendering software utilizes standardtechniques, such as the well-known Z buffer algorithm, to draw images of3-D computer models according to some specified point of view.

As is well known in the art, computer 130 also typically includes inputdevices 145 through which physician 20 can interact with the computer.Input devices 145 preferably comprise the sort of computer input devicesgenerally associated with a Silicon Graphics digital computer, e.g.,input devices 145 preferably comprise a keyboard, a mouse, etc. Amongother things, input devices 145 permit physician 20 to initiateoperation of anatomical visualization system 10, to select varioussystem functions, and to supply the system with various directives,e.g., input devices 145 might be used by physician 20 to specify aparticular viewing position for which the application program's imagerendering software should render a visualization of the 3-D softwaremodels contained in database means 70.

Database means 70 comprise a data storage device or medium 150containing one or more 3-D computer models (schematically illustrated as160 in FIG. 1) of the anatomical objects 30 which are to be visualizedby anatomical visualization system 10. The specific data structure usedto store the 3-D computer models 160 will depend on the specific natureof computer 130 and on the particular operating system software 135 andthe particular application program software 140 being run on computer130. In general, however, the 3-D computer models 160 contained in datastorage device or medium 150 are preferably structured as a collectionof software objects. By way of example, a scanned anatomical structuresuch as a human knee might be modeled as three distinct softwareobjects, with the tibia being one software object (schematicallyrepresented at 30A' in FIG. 4), the femur being a second software object(schematically represented at 30B' in FIG. 4), and the meniscus being athird software object (schematically represented at 30C' in FIG. 4).Such software objects are of the sort well known in the art and may havebeen created, for example, through post-processing of CT or MRI scans ofthe patient using techniques well known in the art.

By way of example, in the case where digital computer 130 comprises aSilicon Graphics digital computer of the sort described above, and wherethe operating systems's software comprises the IRIX operating system andthe application program's image rendering software comprises the Iris g1or OpenGL image rendering software, the 3-D computer models 160 mightcomprise software objects defined as polygonal surface models, sincesuch a format is consistent with the aforementioned software. By way offurther example, FIGS. 2 and 3 illustrate a typical manner of defining asoftware object using a polygonal surface model of the sort utilized bysuch image rendering software. In particular, FIG. 2 illustrates thevertices of a unit cube set in an X-Y-Z coordinate system, and FIG. 3illustrates the data file format of the polygonal surface model for thissimple unit cube. As is well known in the art, more complex shapes suchas human anatomical structures can be expressed in corresponding terms.It is also to be appreciated that certain digital computers, such as aSilicon Graphics digital computer of the sort described above, can beadapted such that digital video data of the sort output by videoprocessing means 95 can be made to appear on the surface of a polygonalsurface model software object in the final rendered image using the wellknown technique of texture mapping.

Display means 80 comprise a video display of the sort well known in theart. More particularly, display means 80 comprise a video display 170 ofthe sort adapted to receive video signals representative of an image andto display that image on a screen 180 for viewing by physician 20. Byway of example, video display 170 might comprise a television type ofmonitor, or it might comprise a head-mounted display or a boom-mounteddisplay, or it might comprise any other display device of the sortsuitable for displaying an image corresponding to the video signalsreceived from computer means 60, as will hereinafter be described infurther detail. In addition, where video display 170 comprises ahead-mounted display or a boom-mounted display or some other sort ofdisplay coupled to the physician's head movements, physician trackingmeans 185 comprising a tracking system 187 similar to the trackingsystem 97 described above) may be attached to video display 170 and thenused to advise computer 130 of the physician's head movements. This canbe quite useful, since the anatomical visualization system 10 can usesuch physician head movements to specify a particular viewing positionfor which the application program's image rendering software shouldrender a visualization of the 3-D software models contained in databasemeans 70.

In addition to the foregoing, it should also be appreciated that surgeontracking means 188 (comprising a tracking system 189 similar to thetracking system 97 described above) may be attached directly to surgeon20 and then used to advise computer 130 of the physician's movements.Again, the anatomical visualization system can use such physicianmovements to specify a particular viewing position for which theapplication program's image rendering software should render avisualization of the 3-D software models contained in database means 70.

As noted above, an important aspect of the present invention is theprovision of an improved anatomical visualization system which isadapted to augment a standard video endoscopic system with a coordinatedcomputer model visualization system so as to enhance the physician'sunderstanding of the patient's interior anatomical structure. Inparticular, the improved anatomical visualization system is adapted toaugment the direct, but somewhat limited, video images generated by astandard video endoscopic system with the indirect, but somewhat moreflexible, images generated by a computer model visualization system.

To this end, and referring now to FIG. 1, database means 70 alsocomprise one or more 3-D computer models (schematically illustrated at190 in FIG. 1) of the particular endoscope 90 which is included inanatomical visualization system 10. Again, the specific data structureused to store the 3-D computer models 190 representing endoscope 90 willdepend on the specific nature of computer 130 and on the particularoperating system software 135 and the particular application programsoftware 140 being run on computer 130. In general, however, the 3-Dcomputer models 190 contained in data storage device or medium 150 arepreferably structured as a pair of separate but interrelated softwareobjects, where one of the software objects represents the physicalembodiment of endoscope 90, and the other of the software objectsrepresents the video image acquired by endoscope 90.

More particularly, the 3-D computer models 190 representing endoscope 90comprises a first software object (schematically represented at 90A' inFIG. 4) representative of the shaft of endoscope 90.

The 3-D computer models 190 representing endoscope 90 also comprise asecond software object (schematically represented at 90B' in FIG. 4)which is representative of the video image acquired by endoscope 90.More particularly, second software object 90B' is representative of aplanar disk defined by the intersection of the endoscope's field of viewwith a plane set perpendicular to the center axis of that field of view,wherein the plane is separated from the endoscope by a distance equal tothe endoscope's focal distance. See, for example, FIG. 11, which showshow the optical parameters for an endoscope can define the relationshipbetween the endoscope 90A' and the disk 90B'. In addition, and as willhereinafter be described in further detail, the anatomical visualizationsystem 10 is arranged so that the video signals output by endoscope 90are, after being properly transformed by video processing means 95 intothe digital data format required by digital computer 130, texture mappedonto the planar surface of disk 90B'. Thus it will be appreciated thatsoftware object 90B' will be representative of the video image acquiredby endoscope 90.

Furthermore, it will be appreciated that the two software objects 90A'and 90B' will together represent both the physical structure ofendoscope 90 and the video image captured by that endoscope.

By way of example, in the case where digital computer 130 comprises aSilicon Graphics computer of the sort described above, and where theoperating system's software comprises the IRIX operating system and theapplication program's image rendering software comprises the Iris g1 orOpenGL image rendering software, the 3-D computer models 190 mightcomprise software objects defined as polygonal surface models, sincesuch a format is consistent with the aforementioned software.Furthermore, in a manner consistent with the aforementioned software, UVtexture mapping parameters are established for each of the vertices ofthe planar surface disk 90B' and the digitized video signals fromendoscope 90 are assigned to be texture map images for 90B'. See, forexample, FIG. 10, which is a schematic representation of a unit disksoftware object where the disk is defined in the X-Y plane and has adiameter of 1.

It is important to recognize that, so long as the opticalcharacteristics of endoscope 90 remain constant, the size and positionalrelationships between shaft software object 90A' and disk softwareobject 90B' will also remain constant. As a result, it can sometimes beconvenient to think of shaft software object 90A' and disk softwareobject 90B' as behaving like a single unit, e.g., when positioning thesoftware objects 90A' and 90B' within 3-D computer models.

In accordance with the present invention, once the anatomical 3-Dcomputer models 160 have been established from anatomical softwareobjects 30A', 30B' and 30C' (representative of the anatomical objects30A, 30B, and 30C which are to be visualized by the system), and oncethe endoscope 3-D computer models 190 have been established from theendoscope software objects 90A' and 90B' (representative of theendoscope and the video image captured by that endoscope), the varioussoftware objects are placed into proper registration with one anotherusing techniqes well known in the art so as to form a cohesive databasefor the application program's image rendering software.

Stated another way, a principal task of the application program is tofirst resolve the relative coordinate systems of all the varioussoftware objects of anatomical 3-D computer models 160 and of endoscope3-D computer models 190, and then to use the application program's imagerendering software to merge these elements into a single composite imagecombining both live video images derived from endoscope 90 with computergenerated images derived from the computer graphics system.

In this respect it will be appreciated that anatomical software objects30A', 30B' and 30C' will be defined in 3-D computer models 160 in thecontext of a particular coordinate system (e.g., the coordinate systemestablished when the anatomical software objects were created), andendoscope software objects 90A' and 90B will be defined in the contextof the coordinate system established by endoscope tracking means 50.

Various techniques are well known in the art for establishing the propercorrespondence between two such coordinate systems. By way of example,where anatomical objects 30A', 30B' and 30C' include unique points ofreference which are readily identifiable both visually and within theanatomical 3-D computer models 160, the tracked endoscope can be used tophysically touch those unique points of reference; such physicaltouching with the tracked endoscope will establish the location of thoseunique points of reference within the coordinate system of theendoscope, and this information can then be used to map the relationshipbetween the endoscope's coordinate system and the coordinate system ofthe 3-D computer models 160. Alternatively, proper software objectregistration can also be accomplished by pointing endoscope 90 atvarious anatomical objects 30A, 30B and 30C and then having the systemexecute a search algorithm to identify the "virtual camera" positionthat matches the "real camera" position. Still other techniques forestablishing the proper correspondence between two such coordinatesystems are well known in the art.

Once the proper correspondence has been established between all of thecoordinate systems, anatomical software objects 30A', 30B' and 30C' andendoscope software objects 90A' and 90B' can be considered tosimultaneously coexist in a single coordinate system in the mannerschematically illustrated in FIG. 4, whereby the application program'simage rendering software can generate images of all of the system'ssoftware objects (e.g., 30A', 30B', 30C', 90A' and 90B') according tosome specified point of view.

Furthermore, inasmuch as the live video output from endoscope 90 istexture mapped onto the surface of disk 90B', the images generated bythe application program's image rendering software will automaticallyintegrate the relatively narrow field of view, live video image dataprovided by endoscope 90 with the wider field of view, computer modelimage data which can be generated by the system's computer graphics.See, for example, FIG. 5, which shows a composite image 200 whichcombines video image data 210 obtained from endoscope 90 with computermodel image data 220 generated by the system's computer graphics.

It is to be appreciated that, inasmuch as endoscope tracking means 50are adapted to continuously monitor the current position of endoscope 90and report the same to digital computer 130, digital computer 130 cancontinuously update the 3-D computer models 190 representing endoscope90. As a result, the images generated by the application program's imagerendering software will remain accurate even as endoscope 90 is movedabout relative to anatomical objects 30.

In addition to the foregoing, it should also be appreciated thatanatomical object tracking means 230 (comprising a tracking system 240generally similar to the tracking system 97 described above) may beattached to one or more of the anatomical objects 30A, 30B and 30C andthen used to advise computer 130 of the current position of thatanatomical object (see, for example, FIG. 1, where tracking system 240has been attached to the patient's tibia 30A and femur 30B). As aresult, digital computer 130 can continually update the 3-D computermodels 160 representing the anatomical objects. Accordingly, the imagesgenerated by the application program's image rendering software willremain accurate even as tibia 30A and/or femur 30B move about relativeto endoscope 90.

FIG. 6 provides additional details on how various elements of systemdata are input into computer means 60 in connection with the system'sgeneration of output video for display on video display 170.

FIG. 7 provides additional details on the methodology employed byanatomical visualization system 10 in connection with rendering a videooutput image for display on video display 170.

The application program software 140 of computer means 60 is configuredso as to enable physician 20 to quickly and easily specify a particularviewing position (i.e., a "virtual camera" position in computer graphicsterminology) for which the application program's image renderingsoftware should render a visualization of the 3-D software modelscontained in database means 70. By way of illustration, FIG. 8 shows atypical Apple Newton screen display 300 which provides various userinput choices for directing the system's "virtual camera". For example,physician 20 may select one of the joystick modes as shown generally at310 for permitting the user to use a joystick-type input device tospecify a "virtual camera" position for the system. Alternatively,physician 20 may choose to use physician tracking means 185 or 187 tospecify the virtual camera position for the system, in which casemovement of the physician will cause a corresponding change in thevirtual camera position. Using such tools, the physician may specify avirtual camera position disposed at the very end of the endoscope'sshaft, whereby the endoscope's shaft is not seen in the rendered image(see, for example, FIG. 5), or the user may specify a virtual cameraposition disposed mid-way back along the length of the shaft, whereby aportion of the endoscope's shaft will appear in the rendered image. See,for example, FIG. 9, which shows a composite image 320 which combinesvideo image data 330 obtained from endoscope 90 with computer modelimage data 340 generated by the system's computer graphics, and furtherwherein a computer graphic representation 350 of the endoscope's shaftappears on the rendered image.

It is to be appreciated that physician 20 may specify a virtual cameraposition which is related to the spatial position and orientation ofendoscope 90, in which case the virtual camera position will move inconjunction with endoscope 90. Alternatively, physician 20 may specify avirtual camera position which is not related to the spatial position andorientation of endoscope 90, in which case the virtual camera positionwill appear to move independently of endoscope 90.

Still referring now to FIG. 8, it is also possible for physician 20 touse slider control 360 to direct the application program's imagerendering software to adjust the field of view set for the computergraphic image data 340 (see FIG. 9) generated by the system's computergraphics.

Additionally, it is also possible for physician 20 to use slider control370 to direct the application program's image rendering software to fadethe density of the video image which is texture mapped onto the face ofdisk software object 90B'. As a result of such fading, the face of thesystem's disk can be made to display an overlaid composite made up ofboth video image data and computer graphic image data, with the relativecomposition of the image being dictated according to the level of fadeselected.

It is also to be appreciated that, inasmuch as the display imagerendered by anatomical visualization system 10 is rendered from acollection of software objects contained in 3-D computer models, it ispossible to render the display image according to any preferred verticalaxis. Thus, for example, and referring now to control 380 in FIG. 8, itis possible to render the display image so that endoscope 90 providesthe relative definition of "up", or so that the real world provides therelative definition of "up", or so that some other object (e.g., theprincipal longitudinal axis of the patient's tibia) provides therelative definition of "up".

It is also to be appreciated that anatomical visualization system 10 canbe configured to work with video acquisition devices other thanendoscopes. For example, the system can be configured to work withminiature ultrasound probes of the sort adapted for insertion into abody cavity. In this situation the video output of the miniatureultrasound probe would be texture mapped onto the face of disk softwareobject 90B'. Alternatively, other types of video acquisition devicescould be used in a corresponding manner.

Also, it is possible to use the foregoing visualization system to renderimages of objects other than anatomical structures. For example, thesystem would be used to provide images from the interior of complexmachines, so long as appropriate 3-D computer models are provided forthe physical structures which are to be visualized.

It is also to be understood that the present invention is by no meanslimited to the particular construction herein set forth, and/or shown inthe drawings, but also comprises any modifications or equivalents withinthe scope of the claims.

What is claimed is:
 1. A real-time computer-based viewing systemcomprising:a database defining a 3-D computer model, said databasecomprising at least a first software object corresponding to a physicalstructure which is to be viewed by said system; sensor means foracquiring real-time data regarding said physical structure when saidphysical structure is located within the data acquisition field of saidsensor means, said sensor means being selectively movable relative tosaid physical structure; generating means for generating a secondsoftware object, said second software object comprising a surface,wherein said surface embodies said real-time data acquired by saidsensor means; registration means for positioning said second softwareobject in registration with said first software object in said 3-Dcomputer model, such that said first and second software objectssimultaneously coexist in a single coordinate system; and processingmeans for generating an image from said first and said second registeredsoftware objects taken from a specified point of view relative to saidsingle coordinate system.
 2. A system according to claim 1 wherein saiddata acquisition field is generally conical, and said second softwareobject is disk-shaped.
 3. A system according to claim 2 wherein saidsensor means are adapted to acquire focused video image data from saidphysical structure, and said generating means are adapted to texture mapsaid video data onto said surface of said second software object. 4.Apparatus according to claim 3 wherein said generating means comprisemeans for varying the opacity of said focused video image data texturemapped onto said surface of said second software object, whereby saidfocused video image data texture mapped onto said surface of said secondregistered software object can be faded relative to the remainder of theimage generated by said processing means.
 5. A system according to claim1 wherein said registration means comprise tracking means fordetermining the spatial positioning and orientation of said sensormeans.
 6. A system according to claim 1 wherein said registration meanscomprise tracking means for determining the spatial positioning andorientation of said physical structure.
 7. A system according to claim 1wherein said system further comprises user input means for selectingsaid specified point of view.
 8. A system according to claim 1 whereinsaid system further comprises user tracking means for determining saidspecified point of view.
 9. A system according to claim 1 wherein saidsensor means comprise an endoscope.
 10. A system according to claim 1wherein said physical structure comprises an interior anatomicalstructure.
 11. A real-time computer-based viewing system comprising:adatabase of software objects defining a 3-D computer model; imagegenerating means for generating an image from said software objectscontained in said database, taken from a specified point of view; meansfor specifying said point of view; and movable sensor means foracquiring real-time data regarding a physical structure, wherein atleast a first one of said software objects contained in said databasecorresponds to said physical structure which is to be viewed by saidsystem; and wherein at least a second one of said software objectscontained in said database comprises a surface, wherein said surfaceembodies real-time data acquired from said physical structure by saidmovable sensor means; and wherein said system further comprisesregistration means for positioning said at least a second one softwareobject in registration with said at least a first one software objectsuch that said at least a first one software object and said at least asecond one software object simultaneously coexist in a single coordinatesystem.
 12. A system according to claim 11 wherein said sensor means hasa generally conical data acquisition field, and said at least a secondone software object is disk-shaped.
 13. A system according to claim 12wherein said sensor means are adapted to acquire focused video data fromsaid physical structure, and said video data is texture mapped onto saidsurface of said disk-shaped software object.
 14. A system according toclaim 11 wherein said registration means comprise tracking means fordetermining the spatial positioning and orientation of said movablesensor means.
 15. A system according to claim 11 wherein saidregistration means comprise tracking means for determining the spatialpositioning and orientation of said physical structure.
 16. A systemaccording to claim 11 wherein said means for specifying said point ofview comprises user tracking means.
 17. A system according to claim 11wherein said means for specifying said point of view comprises usertracking means.
 18. A system according to claim 11 wherein said movablesensor means comprise an endoscope.
 19. A system according to claim 11wherein said physical structure comprises an interior anatomicalstructure.
 20. A method for viewing a physical structure, said methodcomprising the steps of:(A) providing:a database defining a 3-D computermodel, said database comprising at least a first software objectcorresponding to a physical structure which is to be viewed by saidsystem; sensor means for acquiring real-time data regarding saidphysical structure when said physical structure is located within thedata acquisition field of said sensor means, said sensor means beingselectively movable relative to said physical structure; generatingmeans for generating a second software object, said second softwareobject comprising a surface, wherein said surface embodies saidreal-time data acquired by said sensor means; registration means forpositioning said second software object in registration with said firstsoftware object in said 3-D computer model, such that said first andsecond software objects simultaneously coexist in a single coordinatesystem; and processing means for generating an image from said first andsaid second registered software objects taken from a specified point ofview relative to said single coordinate system. (B) positioning saidsensor means so that said physical structure is located within said dataacquisition field, and generating said second software object, andpositioning said second software object in registration with said firstsoftware object in said 3-D computer model, such that said first andsecond software objects simultaneously coexist in a single coordinatesystem; (C) selecting a specified point of view relative to said singlecoordinate system; and (D) generating an image from said softwareobjects contained in said database, taken from said specified point ofview.